Vulcanization of rubber



Patented Dec. 1, 1942 OF E r I r a Williams, Borger, ,Tex., and Bernard Miller Sturgis,Pitman, de Nemours & Com

J assignors to E. I. du Pont pany, Wilmingt n,

DeL, a

I corporation of Delaware 7 i 3 No Drawing. Original a V A Serial'No.'272,608. Divided tion January 25', 1940, Serial pplication May 9, 1939,

and this applica- No. 315,522

: reclaims. 01. 260-784) This invention relates to the' vulcanization-of' rubber and particularly to therefor. r v

Many dithiocarbamic-acids and their salts are well known and'ha've been used and proposed new accelerators for use as accelerators in the vulcanization -of- Such dithiocarbamic acids and their rubber. salts usually have} disadvantagous properties which greatly restrict their use. "'IngeneraLthey are very active at low temperatures such as the temperatures at which the "rubber is processed prior to the vulcanization step whereby they tend to cause prevulcanization or scorchings also, the prior dithiocarbamates and their salts generally have the property of rapidly accelerating the vulcanization of of maximum is heated for extendedperiods oftime, there isa radual decrease in themodulus and usually in the tensile strength of the 'Vulcanizate.

It isan object of the present invention ato rubber; producing vulcanizates properties a relativelyshcr't pe- This latter efiect is known as reversion, and is par-- provide a new class of chemical compounds-not heretofore known. It is a further object of this invention to provide a new class of chemical compounds particularly adapted for accelerating the" vulcanization of rubber. A still furtherobje'ct is to provide an improved method of accelerating the vulcanization of rubber. Other objects are to provide new compositions of matter and to advance the art. Still other objects will appear hereinafter.

The above and other objects may be accom- I plished in accordance with our invention, which comprises preparing salts of dimethylene dithiocarbamic acids, which the basic salt-forming groups is selected from the group of metals, guanidines, secondary amines, tertiary amines,.quaternary ammonium bases and heterocyclic imines containing at least and particularly those salts in s six atoms in the ring. These compounds may be prepared by reacting an ethylene imine with carbon disulfide at temperatures up to about C., and preferably at temperatures between 0 C. and room temperatures. Ethylene imine readily reacts with carbon disulfide. In the presence of excess carbon disulfide, for example, it tends to first form the dithiocarbamic acid, which is unstable at room temperatures, and the salts of which are readily converted to other compounds 5 on heating at temperatures substantially in excess of 227 F. If a smaller amount of carbon disulfide is used, a salt of the dithiocarbamic acid is formed. Stable salts may be formed by treating the ethylene imine with carbon disulfide in the presence of basic materials such as alkali and alkaline earth hydroxides, for example sodium, barium" or zinc hydroxide, guanidines, secondary amines or strongly basic tertiary amines, quaternary ammonium hydroxides and heterocyclic imines such as piperidine, morpholine and hexamethylene imine. We believe that when the, ethylene imine reacts with carbon disulfide at the low temperatures specified, it forms a dithio ;'carbamic acid of the following structure:

In the presence I an analysis salt as follows:

Per cent Per cent While the dimethylene dithio carbemates may celerators at rubber processing temperatures up to about227 F'., and hence lack the prevulcanization or scorching characteristics of'such prior dithio carbamates. dimethylene dithiocarbamates 'of our invention are, extremely active at Furthermore, V the dimethylene important advane higher.

Whilethe broad class of compounds hereinbeforementioned have many desirable characofbasic 'substances, this Calculated Found.

They are distinctly different known'and On the other hand, the

the higher vulcanization j temperatures, such as those of about 274? F. and dithio- Sodium dimethylene dithiocarbamate Zinc dimethylene dithiocarbamate Cadmium dimethylene dithiocarbamate Lead dimethylene dithiocarbamate Diphenylguanidine salt of dimethylene dithiocarbamate Sodium 2,2-dimethyl dimethylene dithiocarbamate Zinc 2,2-dimethyl dimethylene dithiocar-bamate In order to illustrate our inventionrnore clearly, the preferred modes of carrying thesameintc effect and the advantageous results to be obtained thereby, the following examples are given:

Example 1 Sodium dimethylene dithiocarbamatej was. prepared in the following manner. 15.2 grams of carbpndisulfide was dispersed through 100 .cc. oi water.-contaming 0.1 gram of sodium'butyl naphthalene sulfonate, a wetting agent, and 8.0 grams of sodium hydroxide. To this solution, 8.6 grams of ethylene imine was'slowly stirredin at C. The resulting product was a. yellow solution of sodium dimethylene..dithiocarbamate. This was converted to the zinc salt by treatment of the solution with 13.6 grams of zinc chloride. The resulting compound was a stable white powder. This was tested in a compound composed of 100 parts of rubber, 5 parts'of zinc oxide, 3 parts of sulfur, 1 part of stearic acid, and 1 part of the accelerator. After heating for 60 minutes at 227 F. the product was not vulcanized sufliciently to be tested. After 30 minutes at 274 F. the product had a tensile strength of 3800 pounds per square inch and, after 12.0. minutes, 4400 pounds, per square inch.

- Example 2' An experiment similar to Example 1 was carried out in which the zinc chloride was replaced by 18.5 grams of cadmium chloride. The resulting whitepowder did not cause vulcanization in 60 minutes at 227 F., but produced a vulcanizate, having a tensile strength of 3625 pounds per square inch when the compound was ulcanized for 30 minutes at.27.4f F.

Example -3- 21.1 grams of diphenylguanidine'was added to zinc oxide, 1 part of stearic acid, and 3 parts of 30 minutes at 227 F; and

sulfur, gave no cure onlya very slight cure in 60. minutes at 227 F.,

but. gave a vulcanizate having a tensile strength.

of .4810. poundsper square inch after 30 minutes. at 274 F.

Example 4 gramm leof sodium. hydroxide was dissol d. in 400 cc. of water andcooledto room temperure. Tmswassii ed whi l smmmcle. of t ylene. uiine'was a ded, and; hen 11 ram.

- pure gum stock vulcanization after .mOle.0f.2,2-.dimethyl ethylene imine.

hese stock' sw relcured-a e. u tsrobtai esi re um a ed i the i011 moles of carbon disulfide was slowly run in, with cooling. The resulting solution was made neutral to Clayton Yellow test paper and then poured slowly, with stirring, into a solution of .5 gram mole of lead acetate in The brown precipitate waslfiltered off and dried at 50. The yield was of theory'of lead dimcthylene dithiocarbamate. When tested in the used in Example 3, this product gave vulcanizates having properties similar to those of the vulcanizates in Example 2, but no 60' minutes at 227 F.

Example 5 'To a solution of 0.1 gram mole of sodium hydroxide in -100 cc. 'ofwater was added 0.1 gram The solution was. cooled. to 15 C.'and stirred vigorously while 0.1 gram mole of carbon disulfide was run in slowly. A yellow solution was formed which becameneutral t Clayton Yellow. This wasfilteredand 9 ded.slowly, wi.th stirring; to a .solution of 0.5 gram mole of zinc sulfate in. 300 'cc. of water. The white-precipitate formed wasfilteredpfi, washedwithwatenand dried. This zinev 2,2-dimethyl dimethylene ,dithiocarbamate was.

tested in thegum rubber stock used in Exam le 3, using; 1% oil-the..accfleratonomthe rubber, and.

gave no curei n 30 minutes. at. 227 C., ,aproduct in a tens le strength .of l475..p0 d p r square inch alter -6.0 minutes .at 227,F. and a p qducthavina 1a. t nsilclstrength of 38 pounds per qu r inch; tes.at.27 -E--.

In Qrdentcmcn c earlypronertiesot our; compounds; orerpthe compounds fthe pri r. art. :a comparative test was,.marle Withzlhci dimeth .lcner.ditl;flocarbamate,. a.;rep+ esentatixe' Qommundtotoun iinvention,..and.zinc

hexamethylene;rilthipcarbamete; .a: representative ompoundbtthespriomart. memento-carryout these tests... theaiollowing. stocks; were prepared:

Smoked; sheet 100 Zincoxide 5 Carbon black 25- Stearic, acid '3 Acceleratorasindicatedf W na a l s=- Zinc dimethylene-dithioecrba'mate'1 Modum Tensile at; Elon Temp. of cure V Time efiatnzgliggn at break. .I at break Minutes. I 227F; '00 No cure' 274FL I 30;". i' 1150. 3800; 740

Zinc'hercmethylene. dithioc irlvamate Viv/.5 ,7

" M dulus.

Tensile at.

Temp. of cure Time at 500% elongation break at break.

. lllinutes 227 F 60 207.5 4175' 700 274F 30' 2150 4475 080.

after vulcamzing .ior. min.-v

show the. advantageous;

22.1." and 274 Elbiigetibn' l 2,303,593. .From this table, it will be apparentthat thezinc hexamethylene dithiocarbamate, a representative of a normal'dithiocarbamate, gave avery strong: vulcanizationproduct in 60 minutes at 227 F.', while the zinc dimethylene dithiocarbamate, arepresentative of our compounds, produced noivulcanization under the same conditions, even though twice as much of the zinc dimethylene dithiocarbamate was employed. This illustrates the greater safety of our compounds over those of the prior art, as stocks which cure rapidly at 227 F. are too active to be employed successfully in. the commercial manufacture ofimany rubber. articles.

It mayalso be noted from the zinc hexamethylene dithiocarbamate was employed, the modulus figure rapidly decreased after 30 minutes cure.at-2 74 F., whereas when the zinc dimethylene dithiocarbamate of our invention was employed, the modulus number increased and hence showed no sign of reversion. Also, the tensile strength at break decreased rapidlyafter .30 minutes vulcanization when the zinc hexamethylene' dithiocarbamate was employed; whereas the tensile strength increased asthe length-of vulcanization was increased up to QQminutes when thecompound of our invention was employed. r

The above examples and tests are given for illustrative purposes only. It will be readily. apparent to those skilled in the art that many other compounds within the scope of our invention may be produced. Instead of ethylene imine itself, we may employ substituted? ethylene imines to produce the dithiocarbamic acids. The ethylene may contain as substituents on the carbon atoms aliphatic, aromatic, halogen, nitro, amino and other similar groups and the aliphatic and aromatic substituents may also contain halogens or nitro, or amino, or other substituents. Some of the other compounds of our invention are the following:

Potassium dimethylene dithiocarbamate Calcium dimethylene dithiocarbamate Barium dimethylene dithiocarbamate Iron dimethylene dithiocarbamate Monomethylammonium dimethylene dithiocarbamate Dimethylammonium ate Tetramethylammonium dimethylene dithiocarbamate Monoethylammonium dimethylene dithiocarbamate Diethylammonium dimethylene dithiocarbamate Monopropylammonium dimethylene dithiocarbamate Dipropylammonium dimethylene dithiocarbamate Monobutylammonium dimethylene bamate Dibutylammonium dimethylene dithiocarbamate Piperidinium dimethylene dithiocarbamate Ditolylguanidine salt dimethylene dithiocarbamate Morpholine salt dimethylene dithiocarbamate Hexamethylene imine salt dimethylene dithiocarbamate dimethylene dithiocarbamdithiocarand the sodium, potassium, calcium, barium, cad- I mium, zinc, lead, iron, diphenylguanidine, ditolylguanidine, monomethylammonium, dimethylammonium, tetramethylammonium, ethylammonium, propylammonium, butylammonium, piperithertable that when.

2,3-diethyl dimethylene .dithiocarbamic acid v dithiocarbainic 2-ethyl-3-methyl' dimethylene acid 5 j 2-propyl dimethylene dithiocarbarhic .acid

2,3-dipropyl dimethylene dithiocai bamic acid 2methyl-3-propy l dimethylene dithiocarbamic acid 2-butyl dimethylene dithiocarbamicacid 2,3-dibutyl dimethylene dithiocarbamic acid 2 -hexyl dimethylene dithiocarbamic' acid 2,3-dihexyl dimethylenedithiocarbamic acid 2-methyl-3-butyl dimethylene dithiocarbamic acid 2-methyl 3 hexyl J dimethylene I dithiocarbamic acid p 2-ethyl-3-propyl dimethylene dithiocarbamic acid j 2-ethyl-3-butyl dimethylene dithiocarbamic acid 2-ethyl-3-hexyl dimethylene dithiocarbamic acid 2-amyl dimethylene, dithiocarbamic acid 2,3-diamyl dimethylene dithiocarbamic acid 2-butyl-3-amyl dimethylene dithiocarbami'c, acid:

2-phenyl dimethylene dithiocarbamic acid. f' 2,3-diphenyl dimethylene dithiocarbamic acid Z-naphthyl dimethylene dithiocarbamic acid 2,3 dinaphthyl dimethylene dithiocarbamic ci dimethylene dithiocarbam- Z-phenyl-B-riaphthyl ic acid 2,2-diphenyl dimethylene dithiocarbamic acid 2-tolyl dimethylene dithiocarbamic acid 2,3-ditolyl dimethylene dithiocarbamic acid It will thus be apparent that the compounds of our invention, and particularly those devoid of acidic groups, are vulcanization of rubber. They possess the advantage of being extremely safe at processing temperatures, possessing high moduli and tensile strengths when vulcanized at the usual vulcanizing temperatures. They show no tendency tousual basic nitrogen compounds such as the diaryl guanidines, the thiuram sulfides and aldehydeamines. The compounds so activated cause very little vulcanization at 227 but give very strong vulcanizates at the higher vulcanizing temperatures. Our compounds also possess the great advantage of producing vulcanized rubber having a high resistance to deterioration caused by heat and oxygen. They also produce rubber products having particularly good resistance to abrasion and flex cracking. Most of these compounds are solids which can be readily ground to form a fine powder which is readily dispersible in the rubber. They are stable over long periods of time at ordinary room temperatures.

This is a division of our copending application Serial No. 272,608, filed May 9, 1939, for Accelerators for the vulcanization of rubber.

While we have disclosed the preferred embodiments of our invention and the of carrying the same into effect, it will be readily apparent to those skilled in the art that many variations and modifications may be made therein excellent accelerators for the' without departing from the spiritlofvouriinv'ention. Accordingly, we do lnot-rwishi to be limited to the specific embodiments disclosed, but intend to cover our invention broadly asinthe appended claims.

We claim:

1. The method of vulcanizing rubber which comprises incorporating into a rubber mix, prior to vulcanization, a small amount of a salt of a dimethylene dithiocarbamic acid which salt .is devoid ofacidic substituents.

2. The method of vulcanizing rubber which comprises incorporating into a rubber mix, prior to vulcanization, a small amount of a metal salt of a dimethylene dithiocarbamic acid which .salt is devoid of acidicsubstituents.

3. The method of vulcanizingrubber which comprises incorporating into a rubber mix, prior to vulcanization, a small amount of a diarylguanidine salt of a dimethylene dithiocarbamic acid which salt is devoid of acidic substituents.

4. The method of vulcanizing rubber which comprises incorporating into a rubber mix, prior to vulcanization, a small amount of a zinc salt of a dimethylene dithiocarbamic acid which salt is devoid of acidic substituents' 5. The .method .of vulcaniz'ing rubber which comprises incorporating 'into a rubber mix, prior to vulcanization, a small amount of a diphenylguanidine salt of a dimethylene dithiocarbamic acid which salt is devoid of acidic substituents.

6. The method of vulcanizing rubber which comprises incorporating into a rubber mix, prior to vulcanization, a small amount of a salt of dimethylene dithiocarbamici acid which. saltis'.devoid of acidic'rsubstituents.

'7. Rubber havingincorporated' therein a small amount of a salt of adimethylenezdithiocarbamlc acid which salt is devoidof acidic substituents.

8. Rubber having incorporated therein a small amount of a metalsaltof adimethylene dithiocarbamic acid which salt is devoidrof acidic substituents.

9. Rubber having'incorporated thereinwasmall amount of a V diarylguanidine salt of 'a' dimethylene dithiocarbamic acid which lsaltuis devoid of acidic substituents.

10. Rubber having incorporatedltherein asmall amount of azinc salt of a-dimethylenedithlocarbamic acid which salt is devoid of acidic substituents.

11. Rubber having incorporated therein a small amount of a diphenylguanidine salt .ot a dimethylene dithiocarbamic acid which salt is devoid of acidic substituents.

12. Rubber having incorporated-therein a small amount oia salt of Idimethylene dithiocarbamlc acid which salt is devoid'ofacidic substituents.

13. Rubber having incorporatedtherein a small amount of zinc dimethylene dithiocarbamate.

14. Rubber having incorporatedthereina: small amount of the diphenylguanidinesalt of dimeth ylene dithiocarbamic acid.

15. Rubber having incorporated therein a small amount of zinc 2,2-dimethyl dimethylene dithiocarbamate.

, IRA

STURGIS.

WILLIAM BERNARD M. 

